The Design of Low-Latency Random Access Procedure for 5G

To meet the low latency demand of 5G Ultra-Reliable and Low Latency Communications (URLLC), International Telecommunication Union (ITU) specifically required the control plane (CP) latency, i.e., the time for user equipment (UE) to change from Radio Resource Control (RRC)_IDLE state to RRC_CONNECTED state, to be less than 20 ms and also encouraged proposals to further reduce it to less than 10 ms. To fulfill the CP latency target, a novel random access procedure (RAP) design is introduced, in which the message exchange procedure is simplified and the demodulation reference signal (DMRS) is used to represent the UE ID. Simulation results show that each UE completes the RAP in one iteration of the proposed RAP due to its collision-free property. Specifically, with the pro-posed RAP, at least 85% of URLLC users complete the RAP within 10 ms in the worst case.